A retarder is not a medium; it’s a colourless substance that alters the chemical composition of acrylic polymer emulsion paints and slows down the drying time without compromising the integrity of the paint film or changing the colour. The retarder can be a gel or an additive. Sometimes retarders are required to be combined with water before mixing with paint.
Acrylics are fast-drying paints. A thin layer of acrylic paint dries between 20 to 30 minutes. The retarder can slow the drying time up to six times. A longer open time is desirable when reworking and blending using the wet-into-wet techniques. The benefits of using a retarder are apparent when an artist needs to create a smooth and uniform coat over a large area. The retarder can also be used to reduce skinning when a stay wet palette is not handy.
The retarder can be mixed with paint on the palette or applied directly to the surface of the canvas either with a brush or a mist spray bottle. If applied to the surface, the paint is applied on the top of the retarder. Each manufacturer will specify the method and correct amount of retarder to be added to the paints. These requirements must be followed strictly or the paint film will not form properly and result in cracking, flaking, and peeling over time.